Negative regulation of epithelium-neutrophil interactions via activation of CD44

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Interactions between CD44 and Hyaluronan in Leukocyte Trafficking

Recruitment of leukocytes from the bloodstream to inflamed tissues requires a carefully regulated cascade of binding interactions between adhesion molecules on leukocytes and endothelial cells. Adhesive interactions between CD44 and hyaluronan (HA) have been implicated in the regulation of immune cell trafficking within various tissues. In this review, the biology of CD44–HA interactions in cell trafficking is summarized, with special attention to neutrophil recruitment within the liver microcirculation. We describe the molecular mechanisms that regulate adhesion between neutrophil CD44 and endothelial HA, including recent evidence implicating serum-derived hyaluronan-associated protein as an important co-factor in the binding of HA to CD44 under flow conditions. CD44–HA-mediated neutrophil recruitment has been shown to contribute to innate immune responses to invading microbes, as well as to the pathogenesis of many inflammatory diseases, including various liver pathologies. As a result, blockade of neutrophil recruitment by targeting CD44–HA interactions has proven beneficial as an anti-inflammatory treatment strategy in a number of animal models of inflammatory diseases.

Influence of hyaluronic acid on wound healing using composite porcine acellular dermal matrix grafts and autologous skin in rabbits

This study aims to explore the influence of hyaluronic acid (HA) on wound healing during xenogeneic porcine acellular dermal matrix (PADM) composite skin grafting. The results will facilitate the development of methods for improving graft contracture and poor elasticity of composite transplantation. Exogenous HA was added to composite PADM grafts and to thin autologous skin grafts during rabbit full-thickness skin wound repair. The influence of HA on wound healing was evaluated according to its contracture rate and its expression of collagen types I and III. The possible mechanism was then explored based on HA metabolism and vascularisation in the skin graft. The results show that exogenous HA relieves graft contracture on rabbit wound surfaces, increases collagen I and III expression and decreases the ratio between collagen types. HA stimulates the generation of more CD44 receptors to strengthen its enzymolysis. The resulting metabolites promote the vascularisation of the wound surface, which are conducive for mitigating graft contracture, and further improve the composite grafting effect.

The role of CD44 in the acute and resolution phase of the host response during pneumococcal pneumonia

Streptococcus pneumoniae is the most prevalent pathogen causing community-acquired pneumonia. CD44 is a transmembrane adhesion molecule, expressed by a wide variety of cell types, that has several functions in innate and adaptive immune responses. In this study, we tested the hypothesis that CD44 is involved in the host response during pneumococcal pneumonia. On intranasal infection with a lethal dose of S. pneumoniae CD44-knockout (KO) mice showed a prolonged survival when compared with wild-type mice, which was accompanied by a diminished pulmonary bacterial growth and reduced dissemination to distant body sites. Whereas, proinflammatory cytokine responses and lung pathology were not affected, CD44 deficiency resulted in increased early neutrophil influx into the lung. In separate experiments, we confirmed a detrimental role of CD44 in host defense against pneumococci during sublethal pneumonia, as demonstrated by an improved capacity of CD44 KO mice to clear a low infectious dose. In addition, CD44 appeared important for the resolution of lung inflammation during sublethal pneumonia, as shown by histopathology of lung tissue slides. In conclusion, we show here that CD44 facilitates bacterial outgrowth and dissemination during pneumococcal pneumonia, which in lethal infection results in a prolonged survival of CD44 KO mice. Moreover, during sublethal pneumonia CD44 contributes to the resolution of the inflammatory response.

CD44 deficiency is associated with increased bacterial clearance but enhanced lung inflammation during Gram-negative pneumonia

Klebsiella pneumoniae is a frequently isolated causative pathogen in respiratory tract infections. CD44 is a transmembrane adhesion molecule that has been implicated in several immunological processes. To determine the role of CD44 during Klebsiella pneumonia, we intranasally infected wild-type and CD44 knockout (KO) mice with 10(2) to 10(4) colony-forming units of K. pneumoniae or administered Klebsiella lipopolysaccharide. During lethal infection, CD44 deficiency was associated with reduced bacterial growth and dissemination accompanied by enhanced pulmonary inflammation. After infection with lower Klebsiella doses, CD44 KO mice but not wild-type mice demonstrated mortality. After infection with even lower bacterial doses, which were cleared by most mice of both strains, CD44 KO mice displayed enhanced lung inflammation 4 and 10 days postinfection, indicating that CD44 is important for the resolution of pulmonary inflammation after nonlethal pneumonia. In accordance, CD44 KO mice showed a diminished resolution of lung inflammation 4 days after intrapulmonary delivery of lipopolysaccharide. CD44 deficiency was associated with the accumulation of hyaluronan together with reduced gene expression levels of the negative regulators of Toll-like receptor signaling, interleukin-1R-associated kinase M, A20, and suppressor of cytokine signaling 3. In conclusion, the absence of CD44 affects various components and phases of the host response during Klebsiella pneumonia, reducing bacterial outgrowth and dissemination and enhancing pulmonary pathology during lethal infection, and diminishing the resolution of lung inflammation during sublethal infection.

CD44 is protective during hyperoxia-induced lung injury

Patients with acute lung injury or respiratory distress syndrome often require supplemental oxygen to maintain tissue oxygenation; however, this treatment can cause or worsen lung inflammation. CD44 is a transmembrane adhesion molecule that is present on a wide variety of cell types, including leukocytes and parenchymal cells, and is an important player in leukocyte trafficking. The aim of this study was to determine the role of CD44 during hyperoxia-induced (> 95% oxygen) acute lung injury. Whereas all wild-type mice survived the 72-hour observation period, 37.5% of CD44 knockout (KO) mice died. CD44 deficiency was associated with a profound influx of neutrophils into the bronchoalveolar space, in the presence of similar or even lower neutrophil numbers in lung parenchyma, suggesting that CD44 is important for containing neutrophils in the pulmonary interstitium during hyperoxia. In addition, CD44 deficiency resulted in increased IL-6 and keratinocyte-derived chemokine release into bronchoalveolar lavage fluid (BALF). CD44 KO mice further displayed evidence for increased vascular leak and injury of type II respiratory epithelial cells. CD44 protected against bronchial epithelial cell death, as shown by increased epithelial cell necrosis and a trend toward increased BALF nucleosome levels in CD44 KO mice. CD44 can bind and internalize hyaluronic acid (HA), which acts proinflammatory. Concentrations of HA increased in BALF from CD44 KO but not wild-type mice during hyperoxia. These data suggest that CD44 protects against hyperoxia-induced lung injury and mortality by a mechanism that at least in part relies on its ability to clear HA from the bronchoalveolar space.

Transepithelial migration of neutrophils: mechanisms and implications for acute lung injury

The primary function of neutrophils in host defense is to contain and eradicate invading microbial pathogens. This is achieved through a series of swift and highly coordinated responses culminating in ingestion (phagocytosis) and killing of invading microbes. While these tasks are usually performed without injury to host tissues, in pathologic circumstances such as sepsis, potent antimicrobial compounds can be released extracellularly, inducing a spectrum of responses in host cells ranging from activation to injury and death. In the lung, such inflammatory damage is believed to contribute to the pathogenesis of diverse lung diseases, including acute lung injury and the acute respiratory distress syndrome, chronic obstructive lung disease, and cystic fibrosis. In these disorders, epithelial cells are targets of leukocyte-derived antimicrobial products, including proteinases and oxidants. Herein, we review the mechanisms involved in the physiologic process of neutrophil transepithelial migration, including the role of specific adhesion molecules on the leukocyte and epithelial cells. We examine the responses of the epithelial cells to the itinerant leukocytes and their cytotoxic products and the consequences of this for lung injury and repair. This paradigm has important clinical implications because of the potential for selective blockade of these pathways to prevent or attenuate lung injury.

Molecular mechanism of systemic delivery of neural precursor cells to the brain: assembly of brain endothelial apical cups and control of transmigration by CD44

Systemically injected neural precursor cells (NPCs) were unexpectedly shown to reach the cerebral parenchyma and induce recovery in various diffuse brain pathologies, including animal models of multiple sclerosis. However, the molecular mechanisms supporting NPC migration across brain endothelium remain elusive. Brain endothelium constitutes the blood-brain barrier, which uniquely controls the access of drugs and trafficking of cells, including leukocytes, from the blood to the brain. Taking advantage of the availability of in vitro models of human and rat blood-brain barrier developed in our laboratory and validated by us and others, we show here that soluble hyaluronic acid, the major ligand of the adhesion molecule CD44, as well as anti-CD44 blocking antibodies, largely prevents NPC adhesion to and migration across brain endothelium in inflammatory conditions. We present further evidence that NPCs, surprisingly, induce the formation of apical cups at the surface of brain endothelial cells, enriched in CD44 and other adhesion molecules, thus hijacking the endothelial signaling recently shown to be involved in leukocyte extravasation. These results demonstrate the pivotal role of CD44 in the trans-endothelial migration of NPCs across brain endothelial cells: we propose that they may help design new strategies for the delivery of therapeutic NPCs to the brain by systemic administration.

CD44 is highly expressed on milk neutrophils in bovine mastitis and plays a role in their adhesion to matrix and mammary epithelium

Mastitis, inflammation of the mammary gland, is a common and economically important disease in dairy animals. Mammary pathogenic organisms, such as Escherichia coli, invade the teat canal,milk ducts, and mammary alveolar space, replicate in mammary secretions, and elicit a local inflammatory response characterized by massive recruitment of blood polymorphonuclear neutrophil leukocytes (PMN) into the alveoli and milk ducts. CD44 is a trans-membrane glycoprotein previously shown to play a role in mediation and control of blood PMN recruitment in response to inflammatory signals. Here we show, for the first time, increased expression of CD44 on recruited milk PMN in bovine mastitis and the expression of a CD44 variant, CD44v10, on these PMN. Furthermore, we demonstrate that CD44 mediates specific adhesion of bovine blood PMN to hyaluronic acid and mammary epithelial cells. Our results suggest that in mastitis CD44 plays a role in recruiting blood PMN into the mammary glands, the exact nature of this role needs to be elucidated.

Adhesion molecules involved in hepoxilin A3-mediated neutrophil transepithelial migration

A common feature underlying active states of inflammation is the migration of neutrophils (PMNs) from the circulation and across a number of tissue barriers in response to chemoattractant stimuli. Although our group has recently established a discreet role for the PMN chemoattractant, hepoxilin A3 (HXA3) in the process of PMN recruitment, very little is known regarding the interaction of HXA3 with PMNs. To characterize further the event of HXA3-induced PMN transepithelial migration, we sought to determine the adhesion molecules required for migration across different epithelial surfaces (T84 intestinal and A549 airway cells) relative to two well-studied PMN chemoattractants, formyl-methionyl-leucyl-phenylalanine (fMLP) and leukotriene B4 (LTB4). Our findings reveal that the adhesion interaction profile of PMN transepithelial migration in response to HXA3 differs from the adhesion interaction profile exhibited by the structurally related eicosanoid LTB4. Furthermore, unique to PMN transepithelial migration induced by gradients of HXA3 was the critical dependency of all four major surface adhesion molecules examined (i.e. CD18, CD47, CD44 and CD55). Our results suggest that the particular chemoattractant gradient imposed, as well as the type of epithelial cell monolayer, each plays a role in determining the adhesion molecules involved in transepithelial migration. Given the complexities of these interactions, our findings are important to consider with respect to adhesion molecules that may be targeted for potential drug development.

Urothelial CD44 FacilitatesEscherichia coliInfection of the Murine Urinary Tract

Escherichia coli is the most common pathogen found in urinary tract infections (UTIs), mainly affecting children and women. We report that CD44, a hyaluronic acid (HA) binding protein that mediates cell-cell and cell-matrix interactions, facilitates the interaction of E. coli with urothelial cells and thus the infection of the host. We found that CD44 is constitutively expressed on urothelial cells and that HA accumulates in E. coli-induced UTI. In CD44-deficient mice, the bacterial outgrowth was dramatically less compared with wild-type mice despite similar granulocyte influx in the bladder and in the kidney as well as comparable cytokines/chemokines levels in both genotypes. E. coli was able to bind HA, which adhered to CD44-positive tubular epithelial cells. Most importantly, the interaction of CD44 on tubular epithelial cells with HA facilitated the migration of E. coli through the epithelial monolayer. The results provide evidence that CD44 on urothelial cells facilitates E. coli UTI. Disruption of the interaction between CD44 and HA in the bladder may provide a new approach to prevent and to treat UTI.

Targeted deletion of metalloproteinase 9 attenuates experimental colitis in mice: central role of epithelial-derived MMP

BACKGROUND & AIMS

There is mounting evidence that matrix metalloproteinases are the predominant proteinases expressed in the gut mucosa during active inflammatory bowel disease. We investigated the role of metalloproteinase 9 (MMP-9), a secreted gelatinase that is consistently up-regulated in both animal models and human inflammatory bowel disease and is associated with disease severity, in the pathogenesis of colitis by using mice containing a targeted deletion of the MMP-9 gene.

METHODS

Dextran sodium sulfate-induced colitis and Salmonella typhimurium-induced enterocolitis were used as animal models to study colitis.

RESULTS

MMP-9 activity and protein expression were absent from normal colonic mucosa but were up-regulated during experimental colitis. MMP-9-/- mice exposed to dextran sodium sulfate or salmonella had a significantly reduced extent and severity of colitis. Immunohistochemical studies showed that MMP-9 was localized to epithelial cells and granulocytes during active colitis. The immune response to systemic administration of Salmonella typhimurium was not affected in MMP-9-/- mice. Neutrophil transmigration studies and bone marrow chimeras showed that neutrophil MMP-9 is neither required for its migration nor sufficient to induce tissue damage during colitis and that epithelial MMP-9 is important for tissue damage. MMP-9 inhibited cell attachment and wound healing in the model intestinal epithelial cell line, Caco2-BBE.

CONCLUSIONS

Taken together, our data suggest that MMP-9 expressed by epithelial cells may play an important role in the development of colitis by modulating cell-matrix interaction and wound healing. Thus, strategies to inhibit MMP-9 may be of potential therapeutic benefit.

Expression of CD44 and E-cadherin cell adhesion molecules in hypertrophied bladders during chronic partial urethral obstruction and after release of partial obstruction in rats

OBJECTIVES

To determine the functional changes in the bladder and the expression of adhesion molecules in bladder tissue during chronic partial urethral obstruction and after release of partial obstruction in rats.

METHODS

Twenty-one male Sprague-Dawley rats were separated into three groups, each containing 7 rats. A sham operation was performed in group 1 and cystometry was done 6 weeks later. In groups 2 and 3, hypertrophied unstable bladders were developed by partial infravesical outflow obstruction during a 6-week period. After this period, cystometry was performed in all group 2 rats. In group 3, the ligature was removed, the rats were followed up for 6 weeks, and then cystometry was performed. After cystometric evaluation, the bladders in all the rats were removed, weighed, and studied immunohistopathologically.

RESULTS

After release of infravesical outflow obstruction, the bladder weight, residual volume, bladder capacity, maximal voiding pressure, voiding amplitude, and bladder contraction time decreased and bladder compliance increased in group 3 compared with group 2. CD44 and E-cadherin expression in the interstitial space and uroepithelial bladder tissue in group 2 rats stained intensely compared with those of groups 1 and 3.

CONCLUSIONS

After release of 6 weeks of infravesical outflow obstruction, the cystometric parameters were significantly improved. Expression of CD44 and E-cadherin in the obstructed bladder tissue may be a pathologic sign of inflammation.

Role of CD44 and hyaluronan in neutrophil recruitment

Lymphocyte CD44 interactions with hyaluronan localized on the endothelium have been demonstrated to mediate rolling and regulate lymphocyte entry into sites of chronic inflammation. Because neutrophils also express CD44, we investigated the role of CD44 and hyaluronan in the multistep process of neutrophil recruitment. CD44(-/-) and wild-type control mice were intrascrotally injected with the neutrophil-activating chemokine, MIP-2, and leukocyte kinetics in the cremasteric microcirculation were investigated 4 h subsequently using intravital microscopy. Neither the rolling flux nor the rolling velocities were decreased in CD44(-/-) mice relative to wild-type mice. In vitro, neutrophils did not roll on the CD44 ligand hyaluronan, consistent with the in vivo data that CD44/hyaluronan did not mediate rolling. However, the number of adherent leukocytes in the venule was decreased by 65% in CD44(-/-) mice compared with wild-type mice. Leukocyte emigration was also greatly decreased in the CD44(-/-) mice. The same decrease in adhesion and emigration was observed in the wild-type mice given hyaluronidase. Histology revealed neutrophils as being the dominant infiltrating population. We generated chimeric mice that express CD44 either on their leukocytes or on their endothelium and found that CD44 on both the endothelium and neutrophils was important for optimal leukocyte recruitment into tissues. Of those neutrophils that emigrated in wild-type and CD44(-/-) mice, there was no impairment in migration through the interstitium. This study suggests that CD44 can mediate some neutrophil adhesion and emigration, but does not appear to affect subsequent migration within tissues.

Analysis of gender-specific atherosclerosis susceptibility in transgenic[hCETP]25DS rat model

Epidemiological and clinical data demonstrate differences in atherosclerotic coronary heart disease prevalence between age-matched men and premenopausal women. Mechanisms underlying relative athero-susceptibility in men and athero-resistance in premenopausal women remain to be elucidated. Lack of informative animal models hinders research. We report here a moderate-expresser line transgenic for human cholesteryl ester transfer protein (CETP) in the Dahl salt-sensitive hypertensive rat strain, Tg25, that recapitulates premenopausal female athero-resistance. Having ascertained identical genetic background, environmental factors, and equivalent CETP hepatic RNA levels, we detect worse hypercholesterolemia, hypertriglyceridemia, coronary plaques and survival outcome in Tg25 male rats compared with Tg25 females. Hepatic transcription profiles of Tg25 males and females normalized to respective gender- and age-matched non-transgenic controls exhibit significant differences. Genes implicated on hierarchical cluster analysis and quantitative real-time RT-PCR pinpoint pathways associated with coronary plaque progression such as inflammation and arachidonic acid epoxygenation, and not just cholesterol metabolism pathways. The data demonstrate gender-specific factors as key modulators of atherosclerosis phenotype and suggest a possible role for the liver in atheroma progression as a large organ source of proatherogenic systemic factors.

Increased neutrophil influx but no impairment of protective immunity to tuberculosis in mice lacking the CD44 molecule

Up-regulation of expression of the cell-surface marker CD44 is a major characteristic of T lymphocytes responding in the lungs of mice infected with Mycobacterium tuberculosis. These lymphocytes express an activated/memory phenotype as seen by their high expression of the CD44 molecule and low expression of CD62L and CD45RB cell-surface molecules. Based on increasing evidence that the CD44 molecule participates in several aspects of the inflammatory response, we evaluated its role in the response to infection with M. tuberculosis using gene-disrupted mice. In this report, we show that CD44 expression is not necessary for the proper trafficking of protective cells to the lungs of mice infected with M. tuberculosis or the direct expression of protective immunity leading to control and containment of the bacterial load in this organ. However, although there were no differences in the bacterial load or migration of activated T lymphocytes to the inflamed lung, the absence of the CD44 molecule resulted in a substantially increased accumulation of neutrophils in the lung. These data indicate that loss of CD44 expression does not alter expression of T helper cell type 1 immunity to tuberculosis in the lungs but has major effects on the overall cellular composition of the immunopathological response.

Leukocyte–epithelial interactions

As a 'double-edged sword', neutrophil (polymorphonuclear leukocyte) migration across epithelial-lined organs is an important component of host defense, but it also results in epithelial pathophysiology and disease symptoms. There have been significant advances in better understanding the mechanisms of how leukocytes cross the vascular endothelium to exit the bloodstream; however, many of the mechanisms that govern polymorphonuclear leukocyte transepithelial migration are different and we are only just beginning to understand them. Recent findings include new junctional adhesion molecules and carbohydrate moieties as receptors for migrating neutrophils. In addition, new insights into leukocyte-epithelial signaling events have emerged that are beginning to shed light on the role of SIRP-CD47 interactions in regulating the rate of neutrophil transepithelial migration and how neutrophils modulate epithelial barrier function.

Different phenotypes of colon carcinoma cells interacting with endothelial cells: role of E-selectin and ultrastructural data

Adhesion molecules are intimately involved in the process of tumour progression. Among them, E-selectin is an inducible endothelial cell adhesion molecule that plays a role in the interactions of neoplastic cells with the endothelium. These interactions are required for the trans-endothelial migration of tumour cells that leads to the growth at the new sites. Since the detailed events in the early phase of metastasis still remain poorly defined, our study has undertaken an electron-microscopic analysis of the interactions of human colon carcinoma cells with endothelial cells as well as an analysis of the effect of recombinant purified E-selectin in the cell signalling involved in colon cancer cell malignant phenotype. Results revealed that SW480 and T84 colon cancer cell lines show different features, different adhesion kinetics, a different cytoskeletal organization, and a different tyrosine phosphorylation pattern when seeded on an endothelial cell monolayer or recombinant E-selectin. In particular T84 cancer cells adhere more efficiently to the E-selectin and this interaction is associated with pronounced morphological changes, actin redistribution and filopodial processes, and an increase in tyrosine phosphorylation of different proteins. These data support the hypothesis that E-selectin ligand is not only a cell-cell adhesion molecule but also initiates a signalling transduction pathway inside the cells.

CD44 deficiency leads to enhanced neutrophil migration and lung injury in Escherichia coli pneumonia in mice

CD44 is a major cell-surface receptor for hyaluronic acid (HA), a glycosaminoglycan component of extracellular matrix. HA-CD44 interactions have been implicated in leukocyte extravasation into an inflammatory site. This study examined the role of CD44 in acute inflammatory responses during pneumonias induced by Escherichia coli and Streptococcus pneumoniae using CD44-deficient mice. In E. coli-induced pneumonia, neutrophil accumulation in the lungs and edema formation was increased by 84% and 88%, respectively, in CD44-deficient mice compared to wild-type mice. In contrast, no difference was observed between these genotypes in S. pneumoniae-induced pneumonia, and the HA content in the lungs decreased after instillation of S. pneumoniae, but not E. coli, in both genotypes. Studies to determine the mechanisms for this enhanced response showed that: 1) neutrophil apoptosis was not different between these two genotypes in either type of pneumonia; 2) CD44 deficiency resulted in enhanced mRNA expression of several inflammatory genes; and 3) CD44-deficient neutrophils migrated through Matrigel in response to chemoattractants faster and in greater numbers than wild-type neutrophils in vitro and this increase was in part dependent on HA content in the Matrigel. These data demonstrate that CD44 deficiency results in enhanced inflammation in E. coli but not S. pneumoniae-induced pneumonia, suggesting a previously unrecognized role for CD44 in limiting the inflammatory response to E. coli.